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Effects of experimental removal of Barred Owls on population demography of Northern Spotted Owls in Washington and Oregon—2017 progress report

Open-File Report 2018-1086

By:
ORCID iD , ORCID iD , ORCID iD , ORCID iD , and ORCID iD
https://doi.org/10.3133/ofr20181086

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Abstract

Populations of Northern Spotted Owls (Strix occidentalis caurina; hereinafter referred to as Spotted Owl) are declining throughout this subspecies’ geographic range. Evidence indicates that competition with invading populations of Barred Owls (S. varia) has contributed significantly to those declines. A pilot study in California showed that localized removal of Barred Owls coupled with conservation of suitable forest conditions can slow or even reverse population declines of Spotted Owls. It remains unknown, however, whether similar results can be obtained in areas with different forest conditions, greater densities of Barred Owls, and fewer remaining Spotted Owls. During 2015–17, we initiated a before-after-control-impact (BACI) experiment at three study areas in Oregon and Washington to determine if removal of Barred Owls can improve population trends of Spotted Owls. Each study area had at least 20 years of pre-treatment demographic data on Spotted Owls, and represented different forest conditions occupied by the two owl species in the Pacific Northwest. This report describes research accomplishments and preliminary results from the first 2.5 years (March 2015–August 2017) of the planned 5-year experiment.

Suggested Citation

Wiens, J.D., Dugger, K.M., Lesmeister, D.B., Dilione, K.E., and Simon, D.C., 2018, Effects of experimental removal of Barred Owls on population demography of Northern Spotted Owls in Washington and Oregon—2017 progress report: U.S. Geological Survey Open-File Report 2018–1086, 23 p., https://doi.org/10.3133/ofr20181086.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Background and Study Objectives
  • Experimental Study Areas
  • Methods
  • Preliminary Results, March 2015–September 2017
  • Associated Research Activities and Accomplishments
  • Summary
  • Work and Reporting Schedule
  • Acknowledgments
  • References Cited
  • Appendixes 1–2

Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Effects of experimental removal of Barred Owls on population demography of Northern Spotted Owls in Washington and Oregon—2017 progress report
Series title:
Open-File Report
Series number:
2018-1086
DOI:
10.3133/ofr20181086
Year Published:
2018
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Forest and Rangeland Ecosystem Science Center
Description:
iv, 23 p.
Country:
United States
State:
Oregon, Washington
Online Only (Y/N):
Y